${}^5\mathrm{He}$ ternary fission yields of ${}^{252}\mathrm{Cf}$ and ${}^{235}\mathrm{U}\mathrm{}(n,f)\mathrm{}$

The relative ${}^4\mathrm{He}$ and ${}^5\mathrm{He}$ ternary fission yields were determined from a careful analysis of the energy distribution of $\alpha$ spectra from a new measurement with a ${}^{252}\mathrm{Cf}$ source and from published data on ${}^{252}\mathrm{Cf}$ and ${}^{235}\mathrm{U}\mathrm{}(n,f).$ The kinetic energies of the ${}^5\mathrm{He}$ and ${}^4\mathrm{He}$ ternary particles were found to be approximately 11 and 16 MeV, respectively. ${}^5\mathrm{He}$ particles contribute 10–20 % to the total alpha yield with the remainder originating from ${}^4\mathrm{He}$ accompanied fission.